The abovementioned diaphragm taps are particularly employed with bags fabricated of plastic material, such often being bags used to distribute wine. Due to the low surface tension of wine, even small defects in the sealing surface of the spout can result in leakage. Although there is the loss of the wine per se to be considered, an important additional consideration is the damage done to the carton containing the defective tap as well as the stored cartons surrounding it. Thus, considerable loss results from just one defective tap.
A further problem of diaphragm taps is that they cannot easily be pressure tested, so as to detect faults in the moulding of the tap, prior to engagement with the bag.
Still a further problem is that known diaphragm type taps that employ a filling tube use the free end of the tube to sealingly engage the diaphragm so as to prevent liquid from leaking through the tap. Although this is an economical and practical arrangement, since the container is filled by the engagement of a dispensing nozzle with the free end of the filling tube, there is the disadvantage that in practice, if the dispensing nozzle is not properly aligned with the fitting tube at all times, then some damage to the free end of the fitting tube will result. Thus, a further source of possible leaks is the deformation of the free end of the filling tube.